A machine that could make the job of identifying crucial particles of evidence at a crime scene much easier and quicker has been developed by US researchers.

Scientists from Purdue University in the US have created a portable mass spectrometer - a machine that identifies forensic samples, such as blood or explosives, by examining their molecular mass.

It means that the process of taking evidence away to be examined in the lab can be cut dramatically shorter, meaning the police could know sooner the type of crime they are dealing with, or who their chief suspect is.

"We're using water droplets, micro-droplets, as high-velocity projectiles," explained Dr R Graham Cooks, who developed the machine.

"We're spraying them at the sample, dislodging molecules of the sample, and these are being sucked into the mass spectrometer.

"The overall process takes less than a second," he told BBC World Service's Science In Action programme.

Explosive residues

Once collected, the samples can then be analysed in the usual way.

The machine gauges exactly what a sample is made of by accurately measuring the masses of the molecules that make it up.

Mass spectrometry has gradually changed the face of forensics over the last 10 years and I do think this will be an important addition

Dr R Graham Cooks

Dr Cooks explained that mass spectrometry is the "gold standard" technique for identifying chemicals, and it has been used in forensic science for many years to identify tiny traces of substances that can prove guilt or innocence.

The traditional technique involves the laborious preparation of samples in a laboratory, where the mass spectrometers are big and cumbersome.

The samples also have to be specially prepared to be fed into it, in order to be analysed in a vacuum.

"The instrument is delicate, and it has a vacuum system which has to be created and treated gently. The sample has to be inserted into vacuum," Dr Cooks added.

"It's those last steps that we're avoiding in this instrument."

The Purdue team's creation has an additional advantage in that it does not require the vacuum at all.

"A small version of the mass spectrometer is in the field and so we just transfer the sample into the mass spectrometer," he said.

"But the sample is air, in ordinary, ambient air, so you don't do any preparation of the sample, you just look at it how it normally is."

Dr Cooks also explained how he expected his team's invention to change forensic science.

"I think mass spectrometry has gradually changed the face of forensics over the last 10 years and I do think this will be an important addition, and probably one widely used.